The invention concerns rotation-imparting drive unit for rotating a data carrier having a brushless d.c. motor with a permanent-magnet rotor, and a stator having a winding, the winding being formed by one or plural winding coils, a circuit arrangement for controlling the energization of the winding to generate a magnetic field effecting rotary motion of the rotor, and also a reading arrangement for reading signals recorded on the data carrier.
For driving data carriers such as computer data-storage platters use is generally made of a brushless d.c. motor, with a data-carrier-receiving hub preferably being secured directly on the motor's shaft, so that the data carrier be directly driven. In order to assure a reliable, error-free reading of the data signals despite high data recording density, it is necessary to drive the data carrier at a high speed that is uniform; for this purpose, as exact as possible a switchover (commutation) of the current fed to the d.c. motor's stator-winding coils is necessary. For this purpose, known d.c. motors have one or plural sensors (e.g. Hall elements) inside the motor housing in the immediate vicinity of the region of the rotor's magnetic influence, and these are caused to issue signals as a result of the alternation of the magnet field during rotor rotation. A circuit board likewise arranged in the motor housing carries the components of a circuit, to which the sensor output signals are fed, and by means of which commutation of the current for the winding is performed in correspondence thereto.
With drive units for data carriers, a further requirement is that their structural height be as low as possible and this, in the case of d.c. motors of the direct-drive type, basically meaning the axial length of the motor's structure. A manufacturer of such motors therefore must make every effort and adopt every reasonable expedient that would serve to reduce axial height. In addition, there is for the motor manufacturer the always present goal, to be able to make and sell the motor at low cost.